The present invention relates to a ribbon cassette, and more particularly to a ribbon cassette provided with a ribbon supply spool, on which an ink ribbon is wound, a ribbon take up spool for taking up the ink ribbon from the ribbon supply spool, and a simple mechanism for preventing slack in the ink ribbon.
Conventionally, many types of ribbon cassettes, each having a ribbon supply spool and a ribbon take up spool, are proposed. In such kind of ribbon cassettes, slack tends to occur in the ink ribbon since the ribbon supply spool is rotatably disposed in a ribbon cassette and no driving force is applied to the ribbon supply spool to regulate the rotation thereof. When the ribbon cassette is set into a printing device, the slack in the ink ribbon precludes suitable feeding of the ink ribbon from the ribbon cassette and hinders correct printing.
Japanese Patent Application Provisional Publication No. HEI 8-25768 discloses a ribbon cassette that is capable of avoiding the problem mentioned above. In the ribbon cassette disclosed in the above-mentioned publication, a clutch spring is provided to the ribbon supply spool, which applies a back tension to the ink ribbon to prevent slack from occurring therein.
In the meanwhile, the ribbon take up spool has not been considered as an object for providing a mechanism for preventing slack in the ink ribbon. This is because the ribbon take up spool is engaged with and rotated by a driving shaft of the printing device during the printing process and hence does not unintentionally rotate to cause slack in the ink ribbon.
The driving shaft of the printing device, however, often rotates more or less at the time the ribbon cassette is taken out from the printing device. Such a rotation of the driving shaft causes the ribbon take up spool to rotate and generate slack in the ink ribbon.
If the ribbon cassette is set into the printing device without removing the slack in the ink ribbon, the ink ribbon may be jammed within the ribbon cassette and make the ribbon cassette unusable. Thus, the slack in the ink ribbon, which may occur at the time the ribbon cassette is taken out from the printing device, should be removed in advance of setting again the ribbon cassette into the printing device. However, this is a burdensome procedure for a user and the user may often forget it. Even if the user has not forgotten to remove the slack in the ink ribbon, the user may rotate the ribbon take up spool in a direction opposite to that for taking up the ink ribbon, resulting in generating more slack in the ribbon.
Thus, there is a need for a ribbon cassette that is provided with a simple mechanism for preventing slack in the ink ribbon due to unintentional rotation of the ribbon take up spool.